Procedures used to obtain silicone rubber foams at room temperature are described, for example, in Examined Published Japanese Patent No. 45-12675. Conventionally, these procedures consisted either of methods wherein a foaming agent was added in the process of obtaining an ordinary silicone rubber elastic which cures at room temperature, and methods wherein foaming properties were conferred on the actual curing mechanism of a silicone rubber composition which cures at room temperature. An example of the latter type of method is a dehydrogenation reaction between organosilicon compounds with hydrogen atoms directly bonded to silicon atoms, and organosilicon compounds with hydroxyl groups directly bonded to silicon atoms. This dehydrogenation reaction is catalyzed by, for example, quaternary ammonium salts, heavy metal salts of carboxylic acids and alkali metal alkoxides as disclosed in Examined Published Japanese Patent Nos. 33-9297 and 44-8755; hydroxylamine compounds and organosilicon compounds with aminoxy groups directly bonded to silicon atoms as disclosed in Examined Published Japanese Patent No. 54-9794, or platinum compounds as disclosed in Unexamined Published Japanese Patent No. 51-46352. All these methods however suffered from the disadvantage that expansion rate was low and from the fact that foaming was difficult to control. They are therefore unsuitable if it is desired to obtain high adiabatic efficiency.
As a result of intensive attempts to overcome the above problems, the authors of the present invention discovered that by the addition of organosilicon compounds with acetylenic unsaturated groups to the SiH/SiOH dehydrogenation reaction system, the expansion rate could not only easily be increased, but a foaming organopolysiloxane composition curing at room temperature was obtained of which the expansion be properly controlled